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ms5611简介：

官方给出的最大分辨率：10cm

工作电压： 1.8v ~ 3.6v

气压 AD 精度：24位

工作环境：－40 ~ +85°C，10 ~ 1200mbar(毫巴 ＝ 百帕)

通讯接口： I2C/SPI (PS:1 - I2C ; PS:0 - SPI)

焊接条件： <250°C < 40秒

开发环境：

开发板： stm32F4discovery

气压计模块：GY-63(ms5611)

开发工具：window7 ＋ MDK(Keil5.1)

程序依赖模块： I2C／SPI 驱动 (此处使用的i2c通讯接口)

#### MS5611接口及相应寄存器定义－drv_ms5611.h

#include "stdbool.h"#include <math.h>// MS5611, Standard address 0x77#define MS5611_ADDR             0x77#define CMD_RESET               0x1E // ADC reset command#define CMD_ADC_READ            0x00 // ADC read command#define CMD_ADC_CONV            0x40 // ADC conversion command#define CMD_ADC_D1              0x00 // ADC D1 conversion#define CMD_ADC_D2              0x10 // ADC D2 conversion#define CMD_ADC_256             0x00 // ADC OSR=256#define CMD_ADC_512             0x02 // ADC OSR=512#define CMD_ADC_1024            0x04 // ADC OSR=1024#define CMD_ADC_2048            0x06 // ADC OSR=2048#define CMD_ADC_4096            0x08 // ADC OSR=4096#define CMD_PROM_RD             0xA0 // Prom read command#define PROM_NB                 8#define MS5611_OSR_4096_CONV_DELAY       8220   // 8.22ms#define MS5611_OSR_2018_CONV_DELAY       4130   // 4.13ms#define MS5611_OSR_1024_CONV_DELAY       2080   #define MS5611_OSR_512_CONV_DELAY        1060   #define MS5611_OSR_256_CONV_DELAY        540    bool ms5611Init(void);  void ms5611_start_ut(void);void ms5611_get_ut(void);void ms5611_start_up(void);void ms5611_get_up(void);void ms5611_calculate(int32_t *pressure, int32_t *temperature);float getEstimatedAltitude(int32_t baroPressure);

- ms5611 i2c 地址定义，由芯片管脚 CSB 决定.`111011Cx`,其中C为CSB引脚的补码值(取反). `TIP:` **本案例中i2c地址 0x77 并没有把i2c 的读写标志位包括，所以在I2C 读写代码实现时务必手动左移。** - ms5611 官方手册 寄存器地址 说明：#### ms5611 代码实现 － drv_ms5611.c

#include "drv_system.h"#include "drv_i2c.h"#include "drv_ms5611.h"static uint32_t ms5611_ut;  // static result of temperature measurementstatic uint32_t ms5611_up;  // static result of pressure measurementstatic uint16_t ms5611_c[PROM_NB];  // on-chip ROM//static uint8_t ms5611_osr = CMD_ADC_4096;#define PA_OFFSET_INIT_NUM 50   static float Alt_offset_Pa=0; double paOffsetNum = 0; uint16_t  paInitCnt=0;uint8_t paOffsetInited=0;static uint16_t ms5611_prom(int8_t coef_num);  static void ms5611_reset(void);static uint32_t ms5611_read_adc(void);static int8_t ms5611_crc(uint16_t *prom);bool ms5611Init(void){    bool ack = false;    uint8_t sig;    int i;    delayMs(10); // No idea how long the chip takes to power-up, but let's make it 10ms    ack = i2cRead(MS5611_ADDR, CMD_PROM_RD, 1, &sig);    if (!ack)        return false;    ms5611_reset();    // read all coefficients    for (i = 0; i < PROM_NB; i++)        ms5611_c[i] = ms5611_prom(i);    if(ms5611_crc(ms5611_prom) != 0)        return false;return true;}static void ms5611_reset(void){    i2cWrite(MS5611_ADDR, CMD_RESET, 1);    delayMs(10);}/** 读取 ms5611 出厂校准数据*/static uint16_t ms5611_prom(int8_t coef_num){    uint8_t rxbuf[2] = { 0, 0 };    i2cRead(MS5611_ADDR, CMD_PROM_RD + coef_num * 2, 2, rxbuf); // send PROM READ commandreturn rxbuf[0] << 8 | rxbuf[1];}/** 读取 ms5611 采集的 温度/气压(24bit)*/static uint32_t ms5611_read_adc(void){    uint8_t rxbuf[3];    i2cRead(MS5611_ADDR, CMD_ADC_READ, 3, rxbuf); // read ADCreturn (rxbuf[0] << 16) | (rxbuf[1] << 8) | rxbuf[2];} /* * 开始采集温度. */ void ms5611_start_ut(void){    i2cWrite(MS5611_ADDR, CMD_ADC_CONV + CMD_ADC_D2 + CMD_ADC_4096, 1); // D2 (temperature) conversion start!} /*  * 读取出 MS5611 采集的温度AD值  */ void ms5611_get_ut(void){    ms5611_ut = ms5611_read_adc();} /*  * 开始采集气压.  */ void ms5611_start_up(void){    i2cWrite(MS5611_ADDR, CMD_ADC_CONV + CMD_ADC_D1 + CMD_ADC_4096, 1); // D1 (pressure) conversion start!} /*  * 读取出 MS5611 采集的气压AD值  */void ms5611_get_up(void){    ms5611_up = ms5611_read_adc();}/* * 读取的气压&温度AD值转换为实际值并作温度补偿(温度精度:0.01℃，气压精度:0.01mbar) */void ms5611_calculate(int32_t *pressure, int32_t *temperature){    uint32_t press;    int64_t temp;    int64_t delt;    int32_t dT = (int64_t)ms5611_ut - ((uint64_t)ms5611_c[5] * 256);    int64_t off = ((int64_t)ms5611_c[2] << 16) + (((int64_t)ms5611_c[4] * dT) >> 7);    int64_t sens = ((int64_t)ms5611_c[1] << 15) + (((int64_t)ms5611_c[3] * dT) >> 8);    temp = 2000 + ((dT * (int64_t)ms5611_c[6]) >> 23);    if (temp < 2000) { // temperature lower than 20degC        delt = temp - 2000;        delt = 5 * delt * delt;        off -= delt >> 1;        sens -= delt >> 2;        if (temp < -1500) { // temperature lower than -15degC            delt = temp + 1500;            delt = delt * delt;            off -= 7 * delt;            sens -= (11 * delt) >> 1;        }    }    press = ((((int64_t)ms5611_up * sens) >> 21) - off) >> 15;    if (pressure)        *pressure = press;    if (temperature)        *temperature = temp;}/* * ms5611 prom 数据 校验 */static int8_t ms5611_crc(uint16_t *prom){    int32_t i, j;    uint32_t res = 0;    uint8_t zero = 1;    uint8_t crc = prom[7] & 0xF;    prom[7] &= 0xFF00;    // if eeprom is all zeros, we're probably fucked - BUT this will return valid CRC lol    for (i = 0; i < 8; i++) {        if (prom[i] != 0)            zero = 0;    }    if (zero)        return -1;    for (i = 0; i < 16; i++) {        if (i & 1)            res ^= ((prom[i >> 1]) & 0x00FF);        else            res ^= (prom[i >> 1] >> 8);        for (j = 8; j > 0; j--) {            if (res & 0x8000)                res ^= 0x1800;            res <<= 1;        }    }    prom[7] |= crc;    if (crc == ((res >> 12) & 0xF))        return 0;return -1;}/* * 气压解算为高度值(cm) */float getEstimatedAltitude(int32_t baroPressure){    static float Altitude;    if(Alt_offset_Pa == 0){         if(paInitCnt > PA_OFFSET_INIT_NUM){            Alt_offset_Pa = paOffsetNum / paInitCnt;            paOffsetInited=1;        }else        paOffsetNum += baroPressure;          paInitCnt++;         Altitude = 0; return Altitude;    }    Altitude = 4433000.0f * (1 - powf((((float) baroPressure) / Alt_offset_Pa), 0.190295f));return Altitude; }

- 由于气压受温度影响，所以需要进行温度补偿。`void ms5611_calculate(int32_t *pressure, int32_t *temperature)`**温度计算公式：**实际和参考温度之间的差异:

{% katex [displayMode] %}dT = D2 - T_{REF} = D2 - C5*2^{8}{% endkatex %}

实际温度(-40…85°C / 0.01°C的分辨率):

{% katex [displayMode] %}TEMP = 20 + dT*TEMPSENS = 2000 + dT*C6/2^{23}{% endkatex %}

温度补偿下气压计算公式：

实际温度抵消 ：

{% katex [displayMode] %}OFF = OFF_{T1} + TCO*dT = C2*2^{16} + (C4*dT) / 2^{7}{% endkatex %}

实际温度灵敏度 :

{% katex [displayMode] %}SENS = SENS_{T1} + TCS*dT = C1*2^{15} + (C3*dT) / 2^{8}{% endkatex %}

温度补偿后得到的气压值：（10 ～ 1200mbar／ 0.001mbar分辨率）

{% katex [displayMode] %}P = D1*SENS - OFF = (D1*SENS / 2^{21}) / 2^{15}{% endkatex %}

Tip: C1 C2 .. 等值都来自芯片内置的 PROM 数据，在初始化代码时读取

Tip: 并且由于此芯片在 大于20°C下比较准，低于20°C气压误差骤增，所以还必须做二阶温度补偿

• 气压值到高度的解算 float getEstimatedAltitude(int32_t baroPressure)
  气压转换高度公式为：

{% katex [displayMode] %}Altitude = 4 433 000 * [1 - (\frac{p}{p_{0}})^{\frac{1}{5.255}}]{% endkatex %}

tip: Altitude 为高度(cm)； P 为温度补偿后的气压值； {% katex [displayMode] %}P_{0} {% endkatex %}标准大气压(101 325 Pa)或者基准气压。

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完整源码，包含 测试 和 所需的I2C驱动.click here